The present invention relates to a noninvasive method for assisting in determining parameters related to pulse-like physiologic events resulting from a heartbeat, and more particularly to a time-based method for "predetermination" validation of such events.
Examples of physiologic events resulting from a heartbeat include but are not limited to oscillometric pulses, K-sounds, invasive arterial blood-pressure pulses, tonometric non-invasive arterial blood-pressure pulses, plethysmographic pulses due to absorption of infrared and near-infrared light by a living subject's blood, heart sounds, cardiogenic oscillations in thoracic impedance waveforms, cardiogenic oscillations in capnograms, and pulsatile components of the airway pressure waveform. With each such event, there is a clearly detectable pulse-like activity with respect to which predetermined points may be selected for reliable time-relationship examination in accordance with the teachings of the present invention.
To illustrate the present invention, a description thereof will be given in the context of validating oscillometric pulses, with the understanding that the invention may be practiced in connection with heartbeat-related physiologic events such as those mentioned above.
Regarding oscillometry, it is known to measure blood pressure noninvasively by monitoring and analyzing pressure pulsations occurring in a blood-vessel-occluding cuff that has been inflated to a supra-systolic pressure and then gradually deflated in steps to below diastolic pressure.
To provide an accurate method of determining blood pressure, there is a need for addressing the problem of artifact, i.e. non-blood-pressure-induced, pulse-like information. Regardless of what is causing such artifact, it is important to provide a method of determining when pulse-like, or pulsatile, information is true (i.e. blood-pressure induced) and when it is false (i.e. non-blood-pressure induced) so that corresponding monitoring apparatus can be smart enough to recognize the difference and discard the false data.
In circumstances where unmistakenably "true" pulse information is not clearly available, it is important also that the method of the invention accept, alternatively, promising "borderline" information.
Similar artifact issues are involved with other heartbeat-resultant physiologic events.
Various conventional methods have been proposed to deal with the problem of artifact. Such methods include the use of a monitored time relationship between an R-wave from an ECG sensor and an oscillometric pulse from a blood-pressure monitor.
For example, in U.S. Pat. No. 4,974,597 there is disclosed a method of verifying an oscillometric pulse by checking whether a single pulse is detected between successive QRS complexes sensed by an ECG monitor.
U.S. Pat. No. 4,216,779 illustrates a Korotkov-based blood-pressure monitoring system that accepts, preliminarily, a first K-sound if it is detected within a predetermined time period after a heartbeat is detected. Then, the first K-sound is accepted ultimately if a second, later K-sound is detected within the time period.
Other such methods are disclosed in U.S. Pat. Nos. 4,349,034 to Ramsey, III, 4,889,133 to Nelson et al. and 4,949,710 to Dorsett et al., which focus on artifact rejection based on criteria such as pulse slope, pulse period, pulse amplitude, pulse area and pulse-area prediction. These criteria are referred to herein as other preselected criteria. It should be understood that other criteria as used herein may include any conventional criteria, including but not limited to those listed above.
An important object of the present invention is to deal with the above-identified problem by providing an improved method of validating heartbeat-induced physiologic events, such as pulsatile blood-pressure information.
A further object of the invention is to provide a way of validating such information by analyzing, along with other preselected criteria, a time-interval relationship extant between pairs of oscillometric pulses and R-waves.